Use linker extensibility to enable better trimming

global.json

@@ -1,9 +1,9 @@
 {
   "sdk": {
-    "version": "5.0.100-preview.6.20310.4"
+    "version": "5.0.100-preview.7.20330.3"
   },
   "tools": {
-    "dotnet": "5.0.100-preview.6.20310.4",
+    "dotnet": "5.0.100-preview.7.20330.3",
     "runtimes": {
       "dotnet/x64": [
         "2.1.18",

src/Razor/Microsoft.NET.Sdk.Razor/integrationtests/Assert.cs

@@ -519,7 +519,7 @@ private static IEnumerable<string> GetDeclaredTypeNames(string assemblyPath)
         {
             using (var file = File.OpenRead(assemblyPath))
             {
-                var peReader = new PEReader(file);
+                using var peReader = new PEReader(file);
                 var metadataReader = peReader.GetMetadataReader();
                 return metadataReader.TypeDefinitions.Where(t => !t.IsNil).Select(t =>
                 {

src/Razor/Microsoft.NET.Sdk.Razor/integrationtests/Wasm/WasmPublishIntegrationTest.cs

@@ -8,8 +8,8 @@
 using Microsoft.AspNetCore.Razor.Tasks;
 using Microsoft.AspNetCore.Testing;
 using Xunit;
-using ResourceHashesByNameDictionary = System.Collections.Generic.Dictionary<string, string>;
 using static Microsoft.AspNetCore.Razor.Design.IntegrationTests.ServiceWorkerAssert;
+using ResourceHashesByNameDictionary = System.Collections.Generic.Dictionary<string, string>;
 
 namespace Microsoft.AspNetCore.Razor.Design.IntegrationTests
 {
@@ -60,6 +60,8 @@ public async Task Publish_WithDefaultSettings_Works()
                 serviceWorkerPath: Path.Combine("serviceworkers", "my-service-worker.js"),
                 serviceWorkerContent: "// This is the production service worker",
                 assetsManifestPath: "custom-service-worker-assets.js");
+
+            VerifyTypeGranularTrimming(result, blazorPublishDirectory);
         }
 
         [Fact]
@@ -223,6 +225,10 @@ public async Task Publish_WithTrimmingdDisabled_Works()
                 serviceWorkerPath: Path.Combine("serviceworkers", "my-service-worker.js"),
                 serviceWorkerContent: "// This is the production service worker",
                 assetsManifestPath: "custom-service-worker-assets.js");
+
+            // Verify assemblies are not trimmed
+            var loggingAssemblyPath = Path.Combine(blazorPublishDirectory, "_framework", "Microsoft.Extensions.Logging.Abstractions.dll");
+            Assert.AssemblyContainsType(result, loggingAssemblyPath, "Microsoft.Extensions.Logging.Abstractions.NullLogger");
         }
 
         [Fact]
@@ -309,6 +315,8 @@ public async Task Publish_HostedApp_DefaultSettings_Works()
                 serviceWorkerPath: Path.Combine("serviceworkers", "my-service-worker.js"),
                 serviceWorkerContent: "// This is the production service worker",
                 assetsManifestPath: "custom-service-worker-assets.js");
+
+            VerifyTypeGranularTrimming(result, blazorPublishDirectory);
         }
 
         [Fact]
@@ -693,6 +701,21 @@ static string ParseWebFormattedHash(string webFormattedHash)
             }
         }
 
+
+        private void VerifyTypeGranularTrimming(MSBuildResult result, string blazorPublishDirectory)
+        {
+            var loggingAssemblyPath = Path.Combine(blazorPublishDirectory, "_framework", "Microsoft.Extensions.Logging.Abstractions.dll");
+            Assert.FileExists(result, loggingAssemblyPath);
+
+            // ILogger is referenced by the app, so we expect it to be preserved
+            Assert.AssemblyContainsType(result, loggingAssemblyPath, "Microsoft.Extensions.Logging.ILogger");
+            // LogLevel is referenced by ILogger and therefore must be preserved.
+            Assert.AssemblyContainsType(result, loggingAssemblyPath, "Microsoft.Extensions.Logging.LogLevel");
+
+            // NullLogger is not referenced by the app, and should be trimmed.
+            Assert.AssemblyDoesNotContainType(result, loggingAssemblyPath, "Microsoft.Extensions.Logging.Abstractions.NullLogger");
+        }
+
         private static BootJsonData ReadBootJsonData(MSBuildResult result, string path)
         {
             return JsonSerializer.Deserialize<BootJsonData>(

src/Razor/Microsoft.NET.Sdk.Razor/src/CreateBlazorTrimmerRootDescriptorFile.cs

@@ -1,8 +1,10 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Linq;
 using System.Xml;
 using System.Xml.Linq;
 using Microsoft.Build.Framework;
@@ -21,16 +23,27 @@ public class CreateBlazorTrimmerRootDescriptorFile : Task
 
         public override bool Execute()
         {
-            using var fileStream = File.Create(TrimmerFile.ItemSpec);
+            var rootDescriptor = CreateRootDescriptorContents();
+            if (File.Exists(TrimmerFile.ItemSpec))
+            {
+                var existing = File.ReadAllText(TrimmerFile.ItemSpec);
+
+                if (string.Equals(rootDescriptor, existing, StringComparison.Ordinal))
+                {
+                    Log.LogMessage(MessageImportance.Low, "Skipping write to file {0} because contents would not change.", TrimmerFile.ItemSpec);
+                    // Avoid writing if the file contents are identical. This is required for build incrementalism.
+                    return !Log.HasLoggedErrors;
+                }
+            }
 
-            WriteRootDescriptor(fileStream);
-            return true;
+            File.WriteAllText(TrimmerFile.ItemSpec, rootDescriptor);
+            return !Log.HasLoggedErrors;
         }
 
-        internal void WriteRootDescriptor(Stream stream)
+        internal string CreateRootDescriptorContents()
         {
             var roots = new XElement("linker");
-            foreach (var assembly in Assemblies)
+            foreach (var assembly in Assemblies.OrderBy(a => a.ItemSpec))
             {
                 // NOTE: Descriptor files don't include the file extension
                 // in the assemblyName.
@@ -60,10 +73,7 @@ internal void WriteRootDescriptor(Stream stream)
                 OmitXmlDeclaration = true
             };
 
-            using var writer = XmlWriter.Create(stream, xmlWriterSettings);
-            var xDocument = new XDocument(roots);
-
-            xDocument.Save(writer);
+            return new XDocument(roots).Root.ToString();
         }
     }
 }

src/Razor/Microsoft.NET.Sdk.Razor/src/build/netstandard2.0/Microsoft.NET.Sdk.Razor.Components.Wasm.targets

@@ -18,10 +18,13 @@ Copyright (c) .NET Foundation. All rights reserved.
   <UsingTask TaskName="Microsoft.AspNetCore.Razor.Tasks.CreateBlazorTrimmerRootDescriptorFile" AssemblyFile="$(RazorSdkBuildTasksAssembly)" />
 
   <PropertyGroup>
-    <PublishTrimmed Condition="'$(PublishTrimmed)' == ''">true</PublishTrimmed>
     <SelfContained>true</SelfContained>
     <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
 
+    <!-- Trimmer defaults -->
+    <PublishTrimmed Condition="'$(PublishTrimmed)' == ''">true</PublishTrimmed>
+    <TrimMode Condition="'$(TrimMode)' == ''">link</TrimMode>
+
     <StaticWebAssetBasePath Condition="'$(StaticWebAssetBasePath)' == ''">/</StaticWebAssetBasePath>
     <BlazorCacheBootResources Condition="'$(BlazorCacheBootResources)' == ''">true</BlazorCacheBootResources>
 
@@ -46,14 +49,6 @@ Copyright (c) .NET Foundation. All rights reserved.
     <KnownFrameworkReference Remove="Microsoft.AspNetCore.App" />
   </ItemGroup>
 
-  <!-- Temporary workaround until ILLink.targets are updated -->
-  <PropertyGroup Condition=" '$(PublishTrimmed)' == 'true' ">
-    <IntermediateLinkDir Condition=" '$(IntermediateLinkDir)' == '' ">$(IntermediateOutputPath)linked\</IntermediateLinkDir>
-    <IntermediateLinkDir Condition=" !HasTrailingSlash('$(IntermediateLinkDir)') ">$(IntermediateLinkDir)\</IntermediateLinkDir>
-    <!-- Used to enable incremental build for the linker target. -->
-    <_LinkSemaphore>$(IntermediateOutputPath)Link.semaphore</_LinkSemaphore>
-  </PropertyGroup>
-
   <Import Project="Microsoft.NET.Sdk.Razor.Components.ServiceWorkerAssetsManifest.targets" Condition="'$(ServiceWorkerAssetsManifest)' != ''" />
 
   <Target Name="_ScrambleDotnetJsFileName" AfterTargets="ResolveRuntimePackAssets">
@@ -305,18 +300,22 @@ Copyright (c) .NET Foundation. All rights reserved.
     </Copy>
   </Target>
 
-  <Target Name="_CreateBlazorTrimmerRootDescriptorFiles" BeforeTargets="ILLink" AfterTargets="ComputeResolvedFilesToPublishList">
+  <Target Name="_BlazorWasmPrepareForLink" BeforeTargets="PrepareForILLink">
     <PropertyGroup>
       <_BlazorTypeGranularTrimmerDescriptorFile>$(IntermediateOutputPath)typegranularity.trimmerdescriptor.xml</_BlazorTypeGranularTrimmerDescriptorFile>
     </PropertyGroup>
 
     <ItemGroup>
       <_BlazorTypeGranularAssembly
-          Include="@(ResolvedFileToPublish)"
+          Include="@(ManagedAssemblyToLink)"
           Condition="'%(Extension)' == '.dll' AND ($([System.String]::Copy('%(Filename)').StartsWith('Microsoft.AspNetCore.')) or $([System.String]::Copy('%(Filename)').StartsWith('Microsoft.Extensions.')))">
         <Required>false</Required>
         <Preserve>all</Preserve>
       </_BlazorTypeGranularAssembly>
+
+      <ManagedAssemblyToLink
+        IsTrimmable="true"
+        Condition="'%(Extension)' == '.dll' AND ($([System.String]::Copy('%(Filename)').StartsWith('Microsoft.AspNetCore.')) or $([System.String]::Copy('%(Filename)').StartsWith('Microsoft.Extensions.')))" />
     </ItemGroup>
 
     <CreateBlazorTrimmerRootDescriptorFile

src/Razor/test/testassets/blazorwasm/Program.cs

@@ -8,6 +8,7 @@ public static void Main(string[] args)
         {
             GC.KeepAlive(typeof(System.Text.Json.JsonSerializer));
             GC.KeepAlive(typeof(RazorClassLibrary.Class1));
+            GC.KeepAlive(typeof(Microsoft.Extensions.Logging.ILogger));
 #if REFERENCE_classlibrarywithsatelliteassemblies
             GC.KeepAlive(typeof(classlibrarywithsatelliteassemblies.Class1));
 #endif

src/Razor/test/testassets/blazorwasm/blazorwasm.csproj

@@ -26,6 +26,14 @@
     <ProjectReference Include="..\razorclasslibrary\RazorClassLibrary.csproj" />
   </ItemGroup>
 
+  <ItemGroup>
+    <!--
+      We need a Microsoft.* package to verify type granular trimming. We'll pick a fixed version to we can bake in some details about
+      the contents of the package in our tests.
+    -->
+    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="3.1.0" />
+  </ItemGroup>
+
   <ItemGroup>
     <!-- These assets should be treated as static web assets for publish purposes -->
     <Content Include="..\LinkBaseToWebRoot\**\*.js">